Rydberg-Dressed Magneto-optical Trap

Anomalous Directed Percolation on a Dynamic Network Using Rydberg Facilitation

The facilitation of Rydberg excitations in a gas of atoms provides an ideal model system to study epidemic evolution on (dynamic) networks and self-organization of complex systems to the critical point of a nonequilibrium phase transition. Using Monte Carlo simulations and a machine learning algorithm we show that the universality class of this phase transition can be tuned but is robust against decay inherent to the self-organization process. The classes include directed percolation (DP), the most common class in short-range spreading models, and mean-field (MF) behavior, but also different types of anomalous directed percolation (ADP), characterized by rare long-range excitation processes. In a frozen gas, ground state atoms that can facilitate each other form a static network, for which we predict DP universality. With atomic motion the network becomes dynamic by long-range (Lévy-flight type) excitations. This leads to continuously varying critical exponents, varying smoothly between DP and MF values, corresponding to the ADP universality class. These findings also explain the recently observed critical exponent of Rydberg facilitation in an ultracold gas experiment [Helmrich et al., Nature (London) 577, 481 (2020)NATUAS0028-083610.1038/s41586-019-1908-6], which was in between DP and MF values.

Direct Laser Cooling of Rydberg Atoms with an Isolated-Core Transition

We propose a scheme to directly laser cool Rydberg atoms by laser cooling the residual ion core within the Rydberg-electron orbit. The scheme is detailed for alkaline-earth-metal Rydberg atoms, whose ions can be easily laser cooled. We demonstrate that a closed optical cooling cycle can be found despite the perturbations caused by the Rydberg electron and that this cycle can be driven over more than 100  μs to achieve laser cooling. The cooling dynamics with and without the presence of magnetic fields are discussed in detail.

Vibration induced transparency: Simulating an optomechanical system via the cavity QED setup with a movable atom

We simulate an optomechanical system via a cavity QED scenario with a movable atom and investigate its application in the tiny mass sensing. We find that the steady-state solution of the system exhibits a multiple stability behavior, which is similar to that in the optomechanical system. We explain this phenomenon by the opto-mechanical interaction term in the effective Hamiltonian. Due to the dressed states formed by the effective coupling between the vibration degree of the atom and the optical mode in the cavity, we observe a narrow transparent window in the output field. We utilize this vibration induced transparency phenomenon to perform the tiny mass sensing. We hope our study will broaden the application of the cavity QED system to quantum technologies.

Maximized atom number for a grating magneto-optical trap via machine-learning assisted parameter optimization

We present a parameter set for obtaining the maximum number of atoms in a grating magneto-optical trap (gMOT) by employing a machine learning algorithm. In the multi-dimensional parameter space, which imposes a challenge for global optimization, the atom number is efficiently modeled via Bayesian optimization with the evaluation of the trap performance given by a Monte-Carlo simulation. Modeling gMOTs for six representative atomic species - ⁷Li, ²³Na, ⁸⁷Rb, ⁸⁸Sr, ¹³³Cs, ¹⁷⁴Yb - allows us to discover that the optimal grating reflectivity is consistently higher than a simple estimation based on balanced optical molasses. Our algorithm also yields the optimal diffraction angle which is independent of the beam waist. The validity of the optimal parameter set for the case of ⁸⁷Rb is experimentally verified using a set of grating chips with different reflectivities and diffraction angles.

Preparation of Long-Lived, Non-Autoionizing Circular Rydberg States of Strontium

Alkaline earth Rydberg atoms are very promising tools for quantum technologies. Their highly excited outer electron provides them with the remarkable properties of Rydberg atoms and, notably, with a huge coupling to external fields or to other Rydberg atoms while the ionic core retains an optically active electron. However, low angular-momentum Rydberg states suffer almost immediate autoionization when the core is excited. Here, we demonstrate that strontium circular Rydberg atoms with a core excited in a 4D metastable level are impervious to autoionization over more than a few millisecond time scale. This makes it possible to trap and laser-cool Rydberg atoms. Moreover, we observe singlet to triplet transitions due to the core optical manipulations, opening the way to a microwave to optical quantum interface.

Many-Body Chiral Edge Currents and Sliding Phases of Atomic Spin Waves in Momentum-Space Lattice

Collective excitations (spin waves) of long-lived atomic hyperfine states can be synthesized into a Bose-Hubbard model in momentum space. We explore many-body ground states and dynamics of a two-leg momentum-space lattice formed by two coupled hyperfine states. Essential ingredients of this setting are a staggered artificial magnetic field engineered by lasers that couple the spin wave states and a state-dependent long-range interaction, which is induced by laser dressing a hyperfine state to a Rydberg state. The Rydberg dressed two-body interaction gives rise to a state-dependent blockade in momentum space and can amplify staggered flux-induced antichiral edge currents in the many-body ground state in the presence of magnetic flux. When the Rydberg dressing is applied to both hyperfine states, exotic sliding insulating and superfluid (supersolid) phases emerge. Because of the Rydberg dressed long-range interaction, spin waves slide along a leg of the momentum-space lattice without costing energy. Our study paves a route to the quantum simulation of topological phases and exotic dynamics with interacting spin waves of atomic hyperfine states in momentum-space lattice.

Three-Dimensional Trapping of Individual Rydberg Atoms in Ponderomotive Bottle Beam Traps

We demonstrate three-dimensional trapping of individual Rydberg atoms in holographic optical bottle beam traps. Starting with cold, ground-state ^{87}Rb atoms held in standard optical tweezers, we excite them to nS_{1/2}, nP_{1/2}, or nD_{3/2} Rydberg states and transfer them to a hollow trap at 850 nm. For principal quantum numbers 60≤n≤90, the measured trapping time coincides with the Rydberg state lifetime in a 300 K environment. We show that these traps are compatible with quantum information and simulation tasks by performing single qubit microwave Rabi flopping, as well as by measuring the interaction-induced, coherent spin-exchange dynamics between two trapped Rydberg atoms separated by 40  μm. These results will find applications in the realization of high-fidelity quantum simulations and quantum logic operations with Rydberg atoms.

Variational Spin-Squeezing Algorithms on Programmable Quantum Sensors

Arrays of atoms trapped in optical tweezers combine features of programmable analog quantum simulators with atomic quantum sensors. Here we propose variational quantum algorithms, tailored for tweezer arrays as programmable quantum sensors, capable of generating entangled states on demand for precision metrology. The scheme is designed to generate metrological enhancement by optimizing it in a feedback loop on the quantum device itself, thus preparing the best entangled states given the available quantum resources. We apply our ideas to the generation of spin-squeezed states on Sr atom tweezer arrays, where finite-range interactions are generated through Rydberg dressing. The complexity of experimental variational optimization of our quantum circuits is expected to scale favorably with system size. We numerically show our approach to be robust to noise, and surpassing known protocols.